LED (Light-emitting diode) panel light is an innovative product in the field of semiconductor lighting. It can replace the traditional grille light, and has significant advantages such as energy saving, environmental protection, no glare, long life, and beautiful appearance. The main working principle of the LED panel light is similar to that of the LED backlight source of the LCD (Liquid-crystal display) TV. The LED is installed on the side of the light guide plate. The light is incident from the side wall of the light guide plate, and then propagates forward in the light guide plate by means of total reflection principle. When the total reflection is destroyed due to the light encountering the micro-structure of the surface of the light guide plate during the forward propagation process, part of the light will change the direction of propagation and exit from the upper and lower surfaces of the light guide plate. In order to utilize the light more effectively, a reflective plate is required to be disposed on the lower surface of the light guide plate for reflecting the light emitted from the lower surface back to the upper surface of the light guide plate. Therefore, the reflective sheet and the light guide plate are the core components of the LED panel light. The main technical development trends of LED panel lights are thinning and simple assembly. How to integrate the functions of the reflective sheet and the light guide plate to form an integrated module is an important issue in the field of LED panel lights.
The Chinese patent application CN201510923952.5 discloses a light source module comprising a light guide plate, at least one light emitting element, a reflective sheet and a plurality of gap units. The light guide plate has a first surface, a second surface opposing to the first surface, a light incident surface connecting the first surface and the second surface, and a plurality of optical micro-structures. The light emitting element is located adjacent to the light incident surface. The reflective sheet is attached to the second surface by an adhesive colloid. The gap unit is configured between the light guide plate and the reflective sheet, and the size of these gap units is greater than or equal to 1 micron. The adhesive colloid includes a first adhesive colloid and a second adhesive colloid. The first adhesive colloid is located between these gap units and the light guide plate, and the second adhesive colloid is located between these gap units and the reflective sheet, the gap unit being transparent. The disadvantage is that the first adhesive colloid and the second adhesive colloid form an optical waveguide layer, resulting in two losses of light: (1) the light originally supposed to propagate in the light guide plate is introduced into the first adhesive colloid layer and is introduced into the second adhesive colloid layer through the transparent gap unit, and the light then propagates forward in the form of total reflection within the first adhesive colloid layer or the second adhesive colloid layer and cannot exit from the front of the light guide plate; (2) the light emitted from the lower surface of the light guide plate obliquely enters into the first adhesive colloid layer or the second adhesive colloid layer, and then propagates forward therein in the form of total reflection and cannot exit from the front of the light guide plate. In addition, the leakage and loss of the light at the position corresponding to the gap unit to the lower surface causes a shadow to be formed at the position viewed from the front of the light guide plate, and the overall optical quality of the panel lamp is deteriorated. U.S. Pat. No. 8,827,526B discloses a method for bonding a reflective sheet or an optical element with a transparent adhesive layer on a side wall of a light guide plate so that a low refractive index transparent layer or an air layer is provided between the reflective sheet and the light outgoing side wall of the light guide plate to ensure the effects of total reflection of light on the side wall. The same disadvantage is that the transparent adhesive layer will form an optical waveguide effect, and the light that should have been transmitted in the light guide plate is transmitted to the transparent adhesive layer, and propagates forward in the form of total reflection within it, and cannot be emitted from the front of the light guide plate, resulting in the loss of light efficiency. In view of this, it is necessary to provide a modular light guide plate scheme with high light extraction efficiency and simple production to realize functional integration of the reflective sheet and the light guide plate.